1. Field of the Invention
The invention relates to a method of, device for, and a control circuit for synchronizing a power supply to a line addressing repetition frequency of a line addressing circuit, the method comprising the steps of: generating trigger moments having a trigger repetition frequency equal to the line addressing repetition frequency, determining an integer larger than zero in dependence upon the trigger repetition frequency, and generating control moments in response to the trigger moments for determining a switching frequency of the power supply, the control moments having a repetition frequency being the trigger repetition frequency divided by the integer.
Such a method and a control circuit for synchronizing a power supply may be applicable in a display system comprising a picture display device and a multiple rate scanning circuit suitable for displaying pictures with different scan rates, as is the case in computer monitors. The power supply may be used to supply stabilized voltages to other circuits of the display system, or to generate an anode voltage for the picture display device.
2. Description of the Related Art
Such a synchronized power supply for a multiple scanning frequency video monitor is known from U.S. Pat. No. 4,516,169. The known display system includes a horizontal deflection circuit which can be operated on two selectable horizontal deflection frequencies. A switching power supply is switched on one optimal switching frequency synchronized to the selected horizontal deflection frequency, independent on which of the two horizontal deflection frequencies occurs. Synchronized operation of the switching supply is desirable to prevent switching of components in the switching power supply from becoming visible on a picture tube of the display system. The known display system shows an embodiment able to cope with two different horizontal deflection frequencies: a second horizontal frequency of 31.5 kilohertz is a first horizontal frequency of 15.75 kilohertz multiplied by two. The switching supply is operated on the first horizontal frequency of 15.75 kilohertz for both horizontal deflection frequencies. A drawback of the known display system is that a fixed switching frequency of the switching supply synchronized to the two horizontal deflection frequencies is only possible if each of the horizontal deflection frequencies is an integer multiple of the fixed switching frequency. The known display system does not offer a practical solution if the display system should be capable of displaying horizontal deflection frequencies which are not an integer multiple of one fixed frequency suitable for switching a switching supply. This can be the case in computer monitors in which the horizontal deflection frequencies, for example, can be 35.2, 37.8, 48, 56, 64, 77.1 or 81.1 kilohertz, respectively.